Oregano...well said. I agree that the debate has (or at least should) move beyond the knowledge we have, and focus on what to do about it. What about the argument that "it's too late to decelerate the change through our actions, so why bother?" Or the argument "what's the big deal about whether sea level rises 4 inches or 2 feet in the next few decades?" Curious to hear your take on those...
In my work (environmental planning consultant), we approach those questions from the perspective of economic risk and how that affects quality of life. What people want more than anything else is predictability. Land developers and investors are no different. I work with those people all the time--if they know the rules, and can reasonably predict long-term results, they will build something. They don't really care what the rules are, they just want to know that they won't change much. In the context of climate change, people behave no differently. Since we know CO2 emissions have spiked through the roof through human actions of the last several decades, and we can see in the long-term record how global temperature tends to respond to CO2 increases from one thing or another, I'm inclined to believe the scientific consensus about what might happen, knowing there are multiple schools of thought on this (that's the nature of science). But the effects are unpredictable...or more accurately, outside the box of our past recent experience.
So as a planner, it would be nice to be able to predict whether a water supply will be reliable in 50 years. Or whether an oceanfront property will still be there in the long haul. These things affect property values, not to mention human health and safety. Yes, some people may benefit from climate change--as you say, longer growing seasons in high latitudes, or easier shipping lanes through the Arctic. So policy becomes a question of risk/reward, and there are many factors that go into formulating policies that respond to that, as you allude to...energy, water supply options, agricultural issues, ethics, safety, but to me the most important of all of these is population dynamics. Not just total population (which is the elephant in the room), but human displacement. Populations (from large ones like tribes, to small ones like families) have always moved in response to stress, and the unpredictable effects of climate change from unprecedented CO2 spikes would surely be one of them. And with displacement comes big costs, both social and economic... and that's the reason people should care about the issue...
In the Glen Canyon region, yes, the Anasazi were likely displaced from their fragile environment by a relatively short drought--it didn't take much in their case--just about 25 years in the late 13th century led to abandoning many of their sites...they were a fairly small population living on the edge to begin with...
1200 BCE: Earliest evidence of the Anasazi is found in the four corners region. This year marks the beginning of the Anasazi Basketmaker (II) Era. 1000 BCE: Archaeologists discover evidence of...
anasaziinfo.weebly.com
...In our case, we're talking about 7.7 billion people and a more global set of changes...
keep it coming Mother Nature! let it snow, let it snow, let it snow... 
